Optical fibers are being increasingly looked to as a medium in which information can be conveniently transmitted by light waves. Such mode of communication offers significant advantages over more conventional transmission media (e.g., copper wire) wherein electrical impulses are utilized. Illustrative examples of the advantages offered by fiber optics include: (a) an increased information transmission capability primarily because of the large available bandwidth, (b) immunity to electromagnetic interference, (c) reduced size and weight, (d) improved transmission security which precludes tapping without detection, and (e) better transmission quality. The optical fibers required for such transmissions commonly are formed of glass or transparent plastic and are recognized commonly to be delicate, brittle, and fragile and to necessitate special measures to insure their safety during installation and use. For instance, excessive bending will irreversibly destroy the usefulness of such fibers and elongations of less than one percent commonly will result in complete breakage (e.g., 0.12 to 0.25 percent elongation to break).
Heretofore when optical fibers have been used in communications applications they have been present in a cable assembly which is intended to provide the required safety for the same. The provision of certain strength or stiffening members within the optical fiber cable has heretofore been recognized to be essential to insure the survival of the delicate optical fibers. For instance, the use of metal wire reinforcement has been proposed in U.S. Pat. Nos. 3,865,466 to Slaughter and 4,110,001 to Olszewski. Other materials such as stainless steel wire, nylon, lyotropic liquid crystalline aramid polymer (e.g., Kevlar poly(p-phenylene terephthalamide), polyethylene, polyethylene terephthalate, cotton, E and S glass/epoxy rods, etc., have also been proposed. See, for instance, U.S. Pat. Nos. 4,037,922 to Claypoole, 4,093,342 to Foord et al, and 4,226,504 to Bellino.
Metal wire reinforcement of the prior art has had the disadvantage of introducing a electrical conductor within the cable assembly which destroys its usefulness for a number of end use applications via electrical interference. Such metallic cable component adds significantly to the weight of the resulting cable thereby militating against handling ease. Also, the metallic component due to thermal expansion and contraction may create problems during use of the cable under varying environmental conditions and to render the cable susceptible to lightning damage.
The use of poly(p-phenylene terephthalamide) as the reinforcement has first necessitated the dissolution of the polymer in an appropriate solvent for the same, and the solution spinning of a large number of relatively fine denier fibers (e.g. thousands of filaments) which may optionally be embedded in an appropriate resin (e.g., an epoxy resin) to form the stiffening member. Such poly(p-phenylene terephthalamide) is incapable of melt extrusion and the procedures required to form the reinforcing member are time consuming, and involve considerable expense. Also, the resulting stiffening member because of the fabrication techniques inherently required is only with difficulty amenable to formation into complex cross-sectional configurations.
Reinforcing members available in the prior art which are composed of E and S glass/epoxy rods are commonly formed by pultrusion and have been found to present shortcomings during service within the resulting cable assembly. For instance, such rods may be susceptible to undesirable thermal expansion and contraction and have tended to be unduly inflexible and relatively brittle which may result in cable failure if the cable assembly is sharply bent.
It is an object of the present invention to provide a novel elongated member suitable for improved service as a stiffening support in an optical fiber cable which is relatively free of shortcomings and disadvantages which reside in the production and service characteristics of the stiffening supports of the prior art.
It is an object of the present invention to provide an elongated member suitable for improved service as a stiffening support in an optical fiber cable.
It is an object of the present invention to provide an elongated member suitable for improved service as a stiffening support in an optical fiber cable which can be economically formed via melt extrusion.
It is an object of the present invention to provide an elongated member suitable for improved service as a stiffening support in an all-dielectric optical fiber cable which can be economically formed via melt extrusion.
It is another object of the present invention to provide an elongated member suitable for improved service as a stiffening support in an optical fiber cable which possesses properties capable of maximizing the survival potential of the delicate optical fiber component of the cable.
It is a further object of the present invention to provide an elongated member suitable for improved service as a stiffening support in an optical fiber cable which exhibits extraordinary dimensional stability at elevated temperatures thereby minimizing potential damage to the delicate optical fibers an making possible the use of the resulting optical fiber cable over a broader temperature range.
These and other objects, as well as the scope, nature, and utilization of the claimed invention will be apparent to those skilled in the art from the following detailed description and appended claims.